Abstract
Mammalian oocytes are surrounded by numerous layers of cumulus cells and the loss of gap junctional communication between cumulus cells and oocytes induces meiotic progression to the MII stage in oocytes. The closure of gap junctional communication was associated with the phosphorylation of connexin-43, gap junctional protein, in cumulus cells. In this study we investigated the effects of the phosphorylation of connexin-43 in cumulus cells on the cAMP level, MAP kinase activity and meiotic progression beyond the MI stage in the oocytes. The connexin-43 in cumulus cells was phosphorylated after 32-hr cultivation of COCs and up to 48 hr, whereas most of the connexin-43 was unphosphorylated in cumulus cells from COCs cultured for 24 hr. When the phosphorylation of connexin-43 in cumulus cells was suppressed by the addition of either PI 3-kinase inhibitor or PKC inhibitor, a significantly higher level of cAMP in the oocyte and a significantly lower proportion of oocytes at the MII stage were produced, as compared to those of oocytes cultured for 48 hr without these drugs. The activity of MAP kinase was also significantly inhibited by the addition of both drugs. It was therefore concluded that the closing of the gap junctional communication via the phosphorylation of connexin-43 might induce a decrease in the cAMP level, resulting in activation of MAP kinase and meiotic progression beyond the MI stage to the MII stage in porcine oocytes.
